An ultrasonic apparatus is an apparatus that transmits ultrasonic waves from a probe to the body surface of an object to be examined, electrically prosesses an echo reflected from the object, forms an ultrasound image (such as B-mode image, M-mode image, D-mode image, or CFM-mode image) from the processed echo signals, and displays the ultrasound images thereof on a monitor.
In such ultrasonic diagnostic apparatus, while a dynamic range that is a sensitivity range generally possible to be displayed on a monitor range is, for instance, between 0 dB˜40 dB, there are cases that the dynamic range of the echo ranges is, for instance, between 0 dB˜90 dB. In this case, when an ultrasound image is displayed on a monitor, there is a need to compress a dynamic ranges of an echo signals.
The difference in signal intensity of the echo signals derived from respective portions in the body organ structure such as a tumor of the liver, gall bladder and diaphragm are relatively small, thus the brightness difference are also small among the pixels that are forming ultrasound images of said organs, which often makes it difficult for the doctors to determine the fine structure of such diagnostic portions upon attempting ultrasonic diagnosis.
Given this factor, a sensitivity graded tomography that repeats the operation a number of times to obtain ultrasound images while changing the sensitivity of the acquired echo signals, and that observes the fine structure by comparing diagnostic portions by the plurality of ultrasound images of different sensitivity, had been conventionally suggested and clinically implemented. This sensitivity graded tomography is described, for example, in [nonpatent document 1].
Nonpatent document 1: The Japan Society of Ultrasonic in Medicine “Ultrasonic Diagnosis”, published by Igaku-Shoin Ltd., in Jul. 15, 1994, p. 398 and p. 887 of first printing of the second edition.
Meanwhile, in the case of displaying ultrasound images by compressing the dynamic range of echo signals such as in the conventional ultrasonic diagnostic apparatus, since there is a possibility that the structures which derive the echo signals of close sensitivity would have the same level of clarity on the screen, it is difficult for the doctors in diagnosing the affected area of the image displayed because of the unobservable difference in clarity level.
In the above-mentioned conventional sensitivity graded tomography, it is necessary to repeat the operations many times to obtain the ultrasound images from an examined portion, and freeze the images obtained on the monitor and to shoot the photographs while changing the overall sensitivity range of the echo signals. Hence it takes much time and energy to obtain the plurality of ultrasound images that have different sensitivity, causing the problem of not being able to execute an efficient diagnose. Also, with conventional sensitivity graded tomography, since the overall sensitivity range of the obtained echo signals had to be displayed to a display dynamic range (display gradation sequence) on the monitor by compressing the range, differentiating echo signals with close sensitivity came along with difficulties.
Moreover, when doctors implement said sensitivity grading tomography, there is a need to change the sensitivity of obtained echo signals, so that the artifacts caused by the side lobe or grating lobe and so forth would not be actualized on the ultrasound images. Thus using said sensitivity grading tomography leaves a problem that the doctors are required to have advanced technique for regulating the apparatus.
The first objective of the present invention is to provide an ultrasonic diagnostic apparatus that makes it possible to observe anatomical features wherein the level of the echo signals are in a narrow range with clear images.
The second objective of the present invention is to provide an ultrasonic diagnostic apparatus that makes it possible to efficiently observe anatomical features wherein the level of echo signals are in a narrow range.
The third objective of the present invention is to provide an ultrasonic diagnostic apparatus that makes it possible to observe anatomical features wherein the level of the echo signals are in a narrow range without requiring doctors to have an advanced technique for regulating the apparatus.